14.08.2013 1 Jyväskylä Summerschool 2013 Wet and Dry Anaerobic Digestion Processes R. Waltenberger, R. Kirchmayr Jyväskylä Summerschool 2013 Definition wet fermentation - Dry matter / total solids (DM / TS) below 15% in the process - Pump able sludge - Mixable sludge - In most cases CSTRs - Requires low DM substrate or good degrading feedstock
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14.08.2013
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Jyväskylä Summerschool 2013
Wet and Dry Anaerobic Digestion ProcessesR. Waltenberger, R. Kirchmayr
Jyväskylä Summerschool 2013
Definition wet fermentation
- Dry matter / total solids (DM / TS) below 15% in the process
- Pump able sludge
- Mixable sludge
- In most cases CSTRs
- Requires low DM substrate or good degrading feedstock
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Definition dry fermentation
- Dry anaerobic digestion is a kind of wrong expression. The microorganisms require of course moist conditions !!!
- According to the feedstock and its properties „Solid state fermentation“ would fit much better.
Dry anaerobic digestion is if not pump able, stackable feedstock with a TS content higher than 30 % is utilized in an AD plant without the addition of external liquids.
- TSfeedstock > 30 %- No external liquids
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Dry Anaerobic Digestion Processes
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Wet anaerobic digestion processes
Jyväskylä Summerschool 2013
Substrate treatment systems for bio waste and residual waste
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Jyväskylä Summerschool 2013
Principle of biological residual waste treatment
or incineration
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Different types of residual waste
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Technologies and design of waste treatment plants
The design of a waste treatment plant is defined by:
- The composition and structure of the input waste• Number of different components in the waste• The particle size distribution• The degree and kind of contamination being possible• Which components shall be recovered• How purified the recovered components should be
- All this information should be available before starting to plan a waste treatment plant. But even then the system should be robustly designed as waste composition and regulations may change quickly.
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Dry fermentation
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Prínciples of dry anaerobic digestion systems
- Dry Digestion in full scale application can be performed in a continuous or discontinuous system.
- Typical feedstock is structure rich material (e.g. municipal organic waste, yard waste, manure fibers, straw, …)
- Compared to liquid fermentation dry AD systems have quite simple process technology and are therefore in most cases cheaper
Jyväskylä Summerschool 2013
Advantages for dry digestion systems
- Very tolerant system for contaminants (sand, fibres, large particles, …)
- Less complex system compared to wet AD systems
- Less maintenance required
- Less critical equipment (pumps, agitation systems, feeding equipment)
- Operation costs may therefore be less compared to wet systems
- Possibility of mobile biogas plants (containers)
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Disadvantages for dry digestion systems
- Special technologies for loading and unloading of the digester necessary
- Not totally mixed
- In discontinuous systems the microbial process has to started for each batch
- In many case lower methane yields compared to wet AD systems (BUT not in
every case)
- In many cases large quantities of structure material is required (a lot of
digester space is consumed for structure material)